Manufacture of wood tubing and the like



June 27, 1944. P. R. GOLDMAN' MANUFACTURE OF woo]: TUBING AND THE LIKEFiled Nov. 28. 1942' I Patented June 27, 1944 MANUFACTURE OF'WOOD TUBINGAND THE LIKE Paul R. Goldman, Andover, Mass., assignor to PlymoldCorporation, Lawrence, Mass, a body corporate Application November 28,1942, Serial No. 467,243

3 Claims.

4 My present invention relates to the manufacture of tubes, pipes andother hollow cylindrical structures having thin wood strips and sheetsas a component material. More particularly the invention, comprisingboth manufacturing processes and products, aims to provide for suchstructures novel constructions, arrangements and combinations ofcomponent means and elements presenting in the resulting articles andproducts distinctive strength and rigidity, both axially and radially,for a given mass and weight of the wood material, and wherein therelation as between fiexure resistance as characterized by axialstrength'and rigidity, on the one hand, and crushing resistance ascharacterized by radial strength and rigidity, on the other hand, may bepredeterminedly selected and calculated as appropriate to different useconditions and requirements.

Products, articles or structures as here concerned form the subjectmatter of my copendlayer is individually wound spirally with a selectedpitch such that the leading and trailing edges of succeeding turns areabutted. Further, each succeeding spiral wrap is wound oppositely totheone preceding, so that the resulting core element-l, Fig. 2, is madeup of the given plurality of layers or .plies individually alternated asto the direction of wind.

ing application Serial No. 526,462, filed March 14, 1944, as a divisionhereof, the claims of this application being directed to novel processesand methods applicable to the manufacture of said new and improvedstructures.

In the accompanying drawing, representing somewhat diagrammatically atypical embodiment of the invention and illustrating the novel processinvolved:

Fig. 1 shows an initial stage of the process, wherein a. tubing core isformed;

Fig. 2 illustrates in cross-section a typical re- 2, the initial phaseor operation in accordance with the invention comprises the formation ofan inner element or core I. For this purpose a re- -movable mandrel M isemployed, of a diameter the same as the inside diameter desired for thecore and for the resulting tube or pipe as a whole. On this mandrelthere is successively wrapped spirally a plurality of layers or laminae,of thin wood stripping or veneer 8, 8a, etc. Each such Thus the sideedge juncture line in any given layer crosses such line of any nextadjacent layer, whether inside or outside it. Desirably also the plieshaving the same direction of wind, such for example as 8, 8b, 8d, etc.,are slightly advanced or set back relative to each other, with resultantstaggering or ofisetting of their spiral joint lines. The number ofwindings, plies or layers for such core element 1 may be varied within aconsiderable range, depending on the wall thickness desired orpermissible in any particular instance. In the majority of cases aboutthree to seven plies are employed, with five representing the averageconstruction, it being understood that the veneer strips such as 8 and8a of Fig. 1 are representative and usually are followed by others suchas 8b, 8c, 8d, Fig. 2, these being similarly applied under alternatedspiraling starting at either end of the plural ply core 'i. Desirably'the individual wood strips or tapes 8, 8a, etc., which may themselves beplural ply in some instances, have the grain or predominant fibredirection disposed lengthwise of the strips, as indicatedat 8g, Fig. 1,so that in the formed core 1 they extend angularly and out of parallelto the core axis.

Each such thin wood layer or wound strip 8, 8a, etc. as spirally laid onthe mandrel is coated with a bonding or plastic agent, such as certainglues, cements or like adhesive or. uniting agents, preferably one ofthe polyme'rizable or plastic type either of the cold setting or theheat setting varieties, depending on the particular field of use for thetubing product in the given instance.

On completion of the winding of the several plies of the core element 1,pressure is applied uniformly to the entire core, either before or afterit is removed from the mandrel M. Such pressure application may-' bevariously accomplished. An effectiveand convenient procedure is found tobe that of temporarily wrapping the core I with a'strip or web ofresilient material 9, Fig; 3, such as a rubber or rubber-likecomposition, wound onto the core under tension proportioned to thedegree of pressure desired. This resilient material 9 desirably not onlyis of a character susceptible of substantial tensioning or stretching inthe course of its application but also is selected with reference to theparticular bonding agent for the core, such as a urea formaldehydeapplication, and also to the temperature conditions for thesetting ordrying treatment which follows: that is, this material 9 for compressionof the core, in the example noted, is resistant to the urea formaldehydeand to heat within the temperature range employed. The compression meanssuch as 9 is removably held at its ends as by suitable ties or clampsnot necessary to illustrate on Fig. 3.

The cores, such as the element 1, with the pressure-applying means suchas 9 in position upon them are then subjected to a drying and setting orpolymerizing treatment. In the case of cold-setting binding agents thismay be accomplished by hanging or otherwise placing the tubing cores soas to subject them to ordinary room temperatures for a period of usually24 to 48 hours, more or less. With heat-setting bonding agents the coreswith the pressure-applying means upon them may be suspended in or passedthrough a drying compartment or oven at controlled temperaturesgenerally of the range of about 180 to 240 depending on the particularagent and on the time available. In general also the polymerization,curing, drying or setting of the cores where relatively coolorcold-setting agents are employed may be considerably accelerated by aheat treatment such as referred to.

Following the drying and setting operation, wherein the compressivepressure such as afforded by the resilient means 9 is maintained, withor without the application of heat, such means is removed from the coreelement 1. This completes the first phase or main operation of theprocess, leaving the core in individually finished condition as acompact and substantially homogenous unit in readiness for thesurrounding outer elements to be described.

It is particularly noted that by reason of the wholly spiral dispositionof th several component veneer strips 8, 8a, etc. of the inner base orcore elements 1, maximum advantage is taken of the compression resistingcapacity of such spirally formed structure. Resultantly these bases orcores 1 are of high rigidity and strength in the radial direction, thatis, against stresses acting radially and tending to crush or deformthem. It is a demonstratable fact that for a given total wall thicknessthe radial strength factor of a cylindrical structure varies with thediameter, being relatively high for the smaller diameters, anddecreasing proportionately with any increase in diameter. Hence byutilizing the inherently radially rigid spiral formation for theinnermost or base element 1, the one having the least internal diameter,the total resulting radial rigidity for the final tubing product ofgiven overall 0! external diameter, is proportionately increased.Otherwise stated, due to its innermost location and consequentrelatively small diameter, adequat radial rigidity is obtained with aless wall thickness and weight of component material. The result is acore or base I which is highly resistant to radial stresses but which isof relatively less rigidity in the axial direction, against forcestending to bend phase or step in the manufacturing process of theinvention. A finished base tube or core I is now itself manipulated inthe manner of a mandrel to receive upon it a longitudinally rigidifyingelement represented as a whole by the numeral Ill. The resultantintermediate structure comprising the base I- and the surroundingelement III will be referred to as the tubing body.

As shown in Fig.4 by way of example, this core-surrounding element Itcomprises one or more wrappings or layers of wood veneer in sheet formwound straight onto the core I, that is, with the side edges of theveneer sheets perpendicular to the core axis. While the veneer for thiscoresurrou'nding element I0 may be of single thickness, preferably itcomprises a plurality of piles, two or more, three of which plies I I, Ila, and l lb are shown in Fig. 4 by way of example. These several veneerplies are first adhesively or otherwise bonded together to provide theplural-ply sheet. Further, the wood material for these sheets isselected and arranged so as to have the grain or .fibre extendpredominately crosswise of the sheet,

as indicated at l2 in Fig. 4, that is, in or approximately inparallelism with the axis of the core as the veneer is wound onto thelatter.

The tubing base or core I has one or more full turns or Wraps of theveneer sheeting l0 applied to it straightwise, that is, with astraight-on wind as above explained. As indicated diagrammatically andin an exaggerated manner at the left in Fig. 5, wherein two turns orlayers of the veneer ID are illustrated by way of example, the leadingand the terminal longitudinal edges of this veneer are disposed in closeradial proximity to each other, so that the entire resultingcore-surrounding element Ill is of uniform thickness, with no excessoverlap or part turns. The individual plies such as H, II a, llb, Fig.4, as also the spirally applied veneer strips 8, 8a, etc. of the tubingbase, generally have a thickness of the order of about /64 to of an inchin the smaller sizes of tubing; that is, tubing of internal diameters offrom say A inch up to 3 or 4 inches. Hence the outward deflection orshouldering of the material of the straight-wound veneer l0 where itpasses from one convolution to the next, as at the left in Fig. 5, isbut a similar small fraction of an inch in radial dimension. But byusing a length of the veneer I0 precalculated to afford exactly thedesired number of winds, or by cutting it off directly opposite theposition of its leading longitudinal edge as applied upon the core, theterminal longitudinal' edge is abutted against and merged with theadjacent shallow shoulder in smooth nonthickening juncture with it.After the following pressure and setting operations the resulting jointis scarcely discernible.

Prior to or during the operation of winding the core-surrounding element[0, it is coated at one or both faces, except at any externally exposedsurface of the final wrap, with a similar impregnating and bonding agentas in connection with the formation of the core I. The resultingcomposite tubing body composed of both the base I and the surroundingelement I0 is then subjected to external pressure uniformly over itsouter cylindrical surface. This again may be variously accomplished, asby temporarily winding onto it under determined tension a resilientpressure strip or web such as that indicated at. 9, Fig. 3, inconnection with forming the core. While maintaining this pressure thecore-surrounding ele- 'ment ill of the tubing body is cured, dried orset,

with or without the application of heat, also as particular usecircumstances maytrequire.

previously described in connection with Figs. 1 to 3. On completion ofthe drying and setting the pressure strip or other compress ve means isremoved, leaving the composite tubing body of Fig. 5 as the intermediateproduct of this second phase, operative step or step series of thepluralphase process as a whole.

Such composite body l-lll has a high radial rigid ty derived primarilyfrom the base I. This is eifectively augmented by the surroundingelement Ill. The latter, however, serves mainly to ail'ord an axialrigidity or fiexure resistance in the resulting product of maximumefilciency wth the given thickness and weight of the component woodmaterial. This is largely due to the determined iact thatfor a givencharacter and thickness of the wood material substantially greaterlongitud nal or axial rigidity is obtained from the straight-on orconvolute wound formation as illustrated in Figs. 4 and 5 and whereinthe natural graining or fibre direction of the veneer is disposed ingeneral parallelism wth the tubing axis. Further, such axial orflexure-resistant strength for a laminate wood cylinder of given wallthickness increases with the diameter of the cylinder; for example, suchtube or cylnder of say 15 in. diameter and having awall thickness of sayin. has a higher longitudinal rigidity, against axial fiexure, than asim larly formed tube or cylinder of say in. diameter with the same wallthickness and material.

Hence, in accordance with the invention, by locating thestraight-gra'ned straight-wound veneer element Ill 1n an outer position,outside the core or base I, and thereby affording it a relatively largerdiameter, the inherent high axial rigid ty factor of such element I ismade to contribute to a maximum extent toward a total axial rigidity forthe resultant wood tubing product of a given material and given insideand overall diameter, wall th ckness and weight. In the resulting tubingbody such as 1|0 the two main elements of thefirst and second phases ofthe process thus cooperatively complement each other to produce astructure of remarkably high ments 1 and Hi the radial and the axialrigidity factors may be proportionately adjusted as any If desired,either or both the operational phases may be repeated one or more times.

With a straight-on application of straightgrained veneer as illustratedand described in connection with Figs. 4 and 5 there is n some instancesa tendency at its outer surface for it to check or crack lengthwise ofthe tubing. To overcome this I complete the tubing by applying to anyexternal straight-laid element such as In of the drawing an outercovering or protective and finishing jacket such as indicated as a wholeby the numeral l3 in Figs. 6 and 7. This may be cation of the bondingagent, temporary install'a tion of the compressive pressure materialsuch as the resilient material 9 of Fig. 3, and the drying and setting,with or without the application of heat, all as explained in detail inconnection with the preceding figures. The end product on removal ofsuch pressure means of this third phase or step of the plural-phaseprocess, is a finished substantially homogeneous tubing unit having hardand wear-resistant surfaces and having the high total radial and .ax alrigidity as above explained.

The methods and processes as herein disclosed and claimed aresusceptible of practice in accordance with the copending jointapplication of Goldman et al., Serial No, 488,854.

My invention either as to process or product is I not limited to theparticular steps or embodiment as herein described or illustrated, itsscope being pointed out in the appendedclaims.

I claim: V

1. In plywood tubing manufacture, that process which comprises incombination the following operational phases and steps: preparing andfurnishing in supply form to be drawn upon a plurality of tape-likewood-veneer strips of indefinitely continuous length arranged to presentthe wood graining predominantly lengthwise in the strips, forming a corestructure by spirally winding about "a removable mandrel a plurality fsuch supply strips respectively in edge-abut ted relation in succeedingadvancing spiral turns and concentrically superposing one strip uponanother in alternated direction of spiral wind in succeeding layers.coating and impregnatingeach spiralled strip layer. with a syntheticresinous heat-and-pressure polymerizable bonding agent. uniformlysubjecting the resulting plural spiral-layer element to heat andpressure maintained pending hard-setting polymerization of the bondingagent, thereby and as a first operational phase providing a plural-layercore-having the directions both of wind and of graining alternatedspirally therein; thereafter laying and wrapping longitudinallystraightwise upon such core one or more concentric layers of wood-veneersheeting formed and arranged to present its graining predominantlylengthwise of the core axis. similarly coating and impregnating andbonding said sheeting and heat and pressure.

t eating it as for the core, thereby and as a second operational phaseto provide in combination with the core a composite tubing body ofsubstantial rigidity and strength both radially and axially; andthereafter and as a third operational phase utilizing such body as awork unit and spirally winding a further plurality of the tapelikewood-veneer strips thereon in alternately opposite directions andsimilarly coating and impregnatlng except for the external surface ofthe final spiral layer and heat-and-pressure bonding such furtheralternated spiral layers as in the core and tubing body forming steps,to Present a complete tubing product.-

2. In plywood tubing manufacture, that process which comprises incombination the following operational phases and steps: preparing andfur-; nishing in supply form to be drawn upon a plurality of tape-likewood-veneer strips of indefinitely continuous length arranged to presentthe wood graining predominantly lengthwise in the strips, forming a corestructure by spirally winding about a removable mandrel a plurality ofsuch supply strips respectively in edge-abutted relamaintained pendinghard-setting polymerization of the bonding agent, thereby and as a firstoperational phase providing a plural-layer core having the directionsboth of wind and of graining alternated spirally therein; thereafterlaying and wrapping longitudinally straightwise upon such core one ormore concentric layers of wood-veneer sheeting formed and arranged topresent its graining predominantly lengthwise of the core axis,similarly supplying a like impregnating and bonding agent between thecore and said sheeting and heat and pressure treating it as for thecore, thereby and as a second operational phase to provide incombination with the core a composite tubing body of substantialrigidity and strength both radially and axially; and thereafter and as athird operational phase utilizing such body as awork unit and spirallywinding' thereon a further wood veneer strip and supplying a like agentbetween it and such tubing body, and impregnating and heat-and-pressurebonding such further spiral winding as in the core and body formingsteps, to present a tubing product subject to any desired finishingtreatment.

3. In plywood tubing manufacture, that process which comprises incombination the followassasas ing operational phases and steps:preparing and furnishing in condition to be drawn upon supplies oftape-like wood-veneer stripping of indefinitely continuous lengtharranged to present the wood graining predominantly lengthwise thereof,spirally winding about a removable mandrel at least one such tape-likewood-veneer strip in edge-abutted non-overlapping relation in succeedingadvancing spiral turns, thereby and as a first operational phase forminga hollow tubular core for the support of succeeding veneer layers,

' and applying thereto a synthetic resinous impregnating and bondingagent adapted for heatand-pressure polymerization; thereafter laying andwrapping longitudinally straightwise upon such core one or moreconcentric layers of woodveneersheeting formed and arranged to presentits graining predominantly lengthwise of the core axis, and-bonding saidsheeting to the core by heat-and-pressure treatment effective upon saidapplied bonding agent, thereby and as a second operational phase toprovide in combination with the core a composite tubing body ofsubstantial rigidity and strength both radially and axially;

and thereafter and as a third operational phase utilizing such body as awork unit and spirally winding thereona further wood-veneer strip andsupplying a like agent between it and such tubing body, and impregnatingand heat-and-pressure bonding such further spiral winding as in thepreceding operational phase, to present a tubing product subject to anydesired finishing treatment.

PAUL R. GOLDMAN.

